The present invention relates to semiconductor devices, and a method for manufacturing a semiconductor device having copper (Cu) interconnects. The present invention relates, in particular, to the formation of Cu interconnections with improved resistance to electromigration (EM). The present invention has particular applicability to high-density semiconductor devices with sub-micron design features.
Recently developed technology has placed more stringent demands on the wiring requirements due to the extremely high circuit densities and faster operating speeds required of such devices. This leads to higher current densities in increasingly smaller conductor lines. As a result, higher conductance wiring is desired which requires either larger cross-section wires for aluminum alloy conductors or a different wiring material that has a higher conductance. The obvious choice in the industry is to develop the latter using pure Cu for its desirable high conductivity. Accordingly, there is a need for electroplating methods, materials, and apparatus that can form very narrow conductive interconnects made from materials such as Cu.
Conventional Cu deposition focuses on the deposition of pure Cu. Recently the addition of dopants to the Cu has attracted attention because of the better resistance of doped Cu to electromigration and stress migration (SM). The dopant element forms intermetallic compounds with the Cu. In such cases, the Cu is typically deposited via a single electroplating process. That is, a single plating solution employing one type of plating chemistry is used to deposit the material that forms the interconnects.
This use of Cu alloys may help solve electromigration problems, but including the dopant throughout the entire interconnect increases the resistivity of the interconnect. This increased resistivity leads to slower performance associated with the semiconductor device.
What is needed is an improved method for forming copper interconnects.